1. Field of the Invention
The present invention relates generally to the field of air filter devices. More particularly, filter devices structured for coupling with a breathing apparatus, such as a respirator or mask or other source of suction, and so as to provide the ability to couple one or more filter elements to a filter platform connected to the breathing apparatus, such that the filter elements and platform function together as an integrated filtering device. More particularly the present invention relates to filter cartridges of the type operable to filter out both particulate matter and to absorb and/or adsorb gases, odors and vapors.
2. Description of the Related Art
When a person is subject to adverse breathing conditions, such as in an environment contaminated with airborne particles and/or harmful vapors, that person""s safety and health will require some type of device for filtering the air before it passes into his or her lungs. To achieve this goal, requirements for such filtering devices have been codified (42 C.F.R. xc2xa7 84) by the National Institute of Occupational Safety and Health (NIOSH). NIOSH regulations were revised to be made substantially more stringent (in June 1995, with a grandfather clause for three years, effective June 1998), to require that these filtering devices demonstrate increased efficiency, a measure of its ability to remove contaminants from air as it is drawn (breathed) through the filtering device.
Historically, improvements in the efficiency of a filtering device have resulted in a concomitant increase in the difference in air pressure between the environment and the interior of the filtering device required for drawing air through it at a given rate. This pressure differential is commonly referred to as pressure drop of the filtering device. Further, increased efficiency in a filtering device also typically has led to a reduction in the effective life span of the filtering device. Consequently, with prior art filtering devices, greater safety through improved filter efficiency has typically made such devices difficult to breathe through and of extremely limited life span. As a result, in addition to breathing discomforts, users experience frequent periods of down time as they must either leave the work area and/or stop working to remove and replace filtering devices.
Accordingly, it has long been a goal of those in the field of filtering devices to develop a filtering device that meets the natural and codified safety requirements of users while demonstrating a pressure drop that is sufficiently low to allow comfortable breathing by the user and, even more importantly, while functioning effectively for a greater period of time.
To attain such improvements, inventors have manipulated the shapes and sizes of the air filters to maximize surface area in the hope that, with increased area over which filtering can be conducted, acceptable efficiency can be realized while at the same time affording the user a low pressure drop and, thus, comfortable breathing. However, filters can be made only so large before they begin to interfere with a user""s vision or mobility. Inventors have also experimented with improved materials in attempted furtherance of the same goals. To date, even slight improvements in efficiency, pressure drop, or life span have been hailed as marked improvements in the art.
One attempt to increase the surface area of the filter is illustrated in U.S. Pat. No. 2,130,555 to Malcolm. The Malcolm patent shows a dust filter unit of a generally tubular form, but having within the unit a filter having a plurality of bellows-like folds. The bellows-like folds provide increased surface area in the filter without the necessity of increasing the diameter of the unit.
The filter unit shown by Malcolm has the advantage of increasing the surface area of the filter medium. However, the folds are part of an integrally formed filter media. Therefore, the design does not permit more or less surface area to be used in accordance with particular needs. Further, the central aperture of each stage reduces the amount of potential surface area of the filter material that is actually used for filtration.
U.S. Pat. No. 2,227,959 to Cover shows a filter composed of three elements connected to one another. The three elements are each structured differently from one another so as to be placed at an assigned position in the filter. However, the device requires specialized innermost and outermost filter elements, which would require that at least three types of filter units be kept in stock at all times. Further the construction of the filter shown in Cover, in which the filter walls are tucked into a cavity in a retaining plate, would be somewhat prone to leakage, compared to modern units in which the filter walls are sealingly engaged to one another around their periphery, and might not meet the more stringent standards in effect today, such as those promulgated by NIOSH. In addition, the central aperture of each stage reduces the amount of potential surface area of the filter material that is actually used for filtration.
U.S. Pat. No. 2,235,624 to Schwartz shows a filter unit for respirators having a cylindrical filter casing of a depth sufficient to hold two disk-shaped filter pads. The filter pad within the casing farthest away from the breathing mask is formed of two circular pads stitched together circumferentially at the edges to form the disk-shaped filter pad, and having an aperture formed through both circular pads to allow a supporting tube element to pass there through. The disk-shaped filter pad closest to the mask is formed similarly but is only apertured on one side. The supporting tube enters the aperture of this innermost pad and comes to an end therein without passing entirely through the innermost pad.
The filter unit taught by Schwartz has several disadvantages. For one thing, the requirement of rigidity of the outer cylindrical filter holder would tend to increase the weight of the mask. Also, the innermost filter pad is of a different construction than the outermost pad, which means that, similar to the situation in the Cover patent, two types of replacement filter elements must be maintained in stock. Further, the central aperture of each stage reduces the amount of potential surface area of the filter material that is actually used for filtration.
U.S. Pat. No. 2,951,551 to West shows an air purifying cannister that is formed from individual filtration units fitted together. Each unit has a male as well as a female connector and a rigid outer wall. The units may be mated in series ad infinitum to form a composite cannister of desired length. Each unit has a tube formed therethrough to allow for the passage of already-filtered air from one unit to the next. The tube is fitted with a cap on the unit farthest from the mask or source of suction to prevent unfiltered air from entering the tube.
The West filter unit, due to the requirement for rigidity, would become very heavy and would be very uncomfortable for the wearer after prolonged use, especially in comparison to the light-weight simple disk filter pad units currently preferred for long term use. Further the weight of the cannister, as additional units are added, would cause a great deal of stress to be applied to the air inlet of any mask using the filter, which may lead to fatigue of the connection materials and eventual breakage. Moreover, the central aperture of each stage reduces the amount of potential surface area of the filter that is actually used for filtration.
A common disadvantage of the types of filter units described above is the high ratio of non-functioning structural materials to functioning filtration material. As a result of this ratio, providing the user with increased filter surface area would result in an associated increase in weight of the filter. Modern filter units are expected to be light in weight, to ensure the comfort of the user.
A prevalent type of light-weight filter pad currently in use is the 3M(copyright) P100 Particulate filter, which consists of a single light-weight disk-shaped unit, formed of two fabric filter pads affixed to one another around the circumference of each pad. One of the filter pads has a central aperture being supported around its periphery by a plastic fastener integrally formed with a bayonet-style female connector, formed to enable a locking connection with a counterpart male connector at the input or inputs of a breathing mask.
However, while the 3M(copyright) P100 filter pad offers the advantage of light weight, due to its construction it can function only as a single unit. Further, because the pad is soft, installation and removal of the filter pad exerts torsional and crushing stress on the filter material as the user grips and twists the filter to engage or disengage the connector that mates with the mask. Moreover, the central aperture reduces the amount of potential surface area of the filter material that is actually used for filtration.
All of the filters discussed above having apertures punched through the filter material lose the filtration benefits of the material that has been punched out. As a result, a significant amount of the potential usable surface area of filter material is lost. Also, all of the filter devices discussed above utilize a direct connection to the respirator, necessitating a compatibility of filter and respirator design.
Further, the types of filters used in the industry currently to filter out gases, odors and/or vapors contain, in addition to filtration materials for filtering out particulate matter, absorbents, adsorbents and other such materials for removing harmful gases or the like. A commonly used adsorbent is activated carbon or charcoal.
Such cartridges typically have an inlet for receiving air to be filtered and an outlet for outputting filtered air and are constructed such that the filtration of the particulates is done at a first stage close to the inlet, by means of filtration material, after which the removal of gases, odors and/or vapors is effected by means of absorbents and/or adsorbents, situated closer to the outlet. Such a physical orientation is described in the industry in terms of the particulate filters residing xe2x80x9cupstreamxe2x80x9d, and the absorbents and/or adsorbents residing xe2x80x9cdownstreamxe2x80x9d. In such a configuration, which is typical of the prior art, the media being filtered, usually air, passes uni-directionally, from the upstream filtration towards the downstream absorbents and/or adsorbents. Examples of such prior art filter cartridges are shown in FIGS. 15A-15C. In each of these figures, AI represents the air inlet side and AO represents the air outlet side of the filter cartridge. FIG. 15C shows the air inlet sides of filters 1 and 2. FIG. 15B shows cartridge 2 with a respirator mask. Note that the receiving end of the mask corresponds to the air outlet side of the cartridge. All of the pictured prior art cartridges have surfaces that are entirely sealed except for the air inlet and outlet ports.
As a result of this uni-directionality, the area available for filtration is quite limited, in particular because in most cases the filters are mounted onto a respiration mask worn over the face of the user. Attempts have been made to increase the available surface area of the upstream filtration material by, for example, the use of pleated folds in the filtering material. However, while such pleating may introduce a deviation in the direction of the air flow, the deviation is negligible for all practical purposes, since air still goes into an inlet and out of an outlet substantially uni-directionally. Moreover, the amount of additional surface area that can be attained in this manner is limited, since only the inlet area can be utilized for this purpose.
As a result of the limited filtration area available in such uni-directional devices, the resulting pressure drop in the filter cartridge will be relatively high, and the efficiency of the filters will be correspondingly low, characteristics that will result in difficult breathing for the user and short life cycle for the filter cartridge.
The provision of a protective casing around the filter, such as is shown in FIGS. 15A-15C, may further limit the surface area available for filtration since typically a sealant is provided between the casing and the filter material, except at the input port.
Also, since people wearing such filters typically are involved in strenuous work, over long hours, breathing difficulties could drastically curtail their ability to carry out their work, and increase their fatigue. In addition, the shorter life cycle of the filters would necessitate frequent changes of the filter cartridges, with a corresponding interruption of work, resulting in a loss of efficiency, work time and quality.
Thus, there is a need for a filter cartridge that has an increased surface area for filtration, while increasing the comfort level of the user, even if a protective casing is required.
Further, there is a need for a filter device structured to permit easy and safe installation and removal of individual filter units, even in a contaminated area. Moreover, there is a need for a filter device having an indirect connection between the filter unit or units and the respirator to allow more flexibility in filter design independent of mask design considerations.
One of the very commonly experienced problems in using presently available breath protection equipment, is the difference in the level of protection experienced from the start of a fresh set of filtering units, and the level of protection and breathing comfort towards or at the end of the expected life cycle (end of life,) of these filter units. Most of these filters and filter units do not have an xe2x80x9cend of lifexe2x80x9d indicator. This leaves it up to the user to estimate the life remaining in a filter, which may result in serious breathing discomfort, and sometimes a lack of protection. All of this can lead to the wearer""s exhaustion, injury and damage to his or her health, and the resulting loss of productivity. As a result, wearers of these filter devices often end up discarding them long before the end of the expected life span, thereby increasing the cost of protection.
Another difficulty faced by users of filtration devices is the requirement that a monitoring of a change of sequence of a particulate and/or gas and vapor filter be performed.
In light of the foregoing, it becomes clear that a filtering device furthering the seemingly incompatible goal of improving efficiency, maximizing the use of available filter material area, while decreasing pressure drop, increasing the effective life span of the filtering device, and allowing for change of sequence monitoring of the filter, would represent a significant advance over the prior art.
In view of the above-mentioned problems of prior art devices, and the needs and concerns of users of filtration devices, it is an object of the present invention to provide a filtering device that demonstrates improved efficiency, maximizing the use of available filter material area, while exhibiting reduced pressure drop, an extended usable life span, and ideally a filter unit structured with absorbents and/or adsorbents to filter gases, odors and/or vapors and to cooperate with a filter platform. The filter unit or units together with the platform form the filter device to be mated to the respirator.
It is another object of the invention to provide a filter platform that can interface the filter units with the respirator and allow for the installation of end of life probes therein, obviating the need for customizing the respirator to provide such functionality, as well as allow for more flexibility in filter unit design due to the presence of the intermediate structure of the filter platform.
It is another object of the present invention to provide each individual wearer the ability to design fit the total filter device to his own comfort level, and at the same time maintain breathing comfort throughout his work period.
It is another object of the present invention to make it possible to keep very low levels of inventory of filters and filter devices, while providing adequate supply at the same time, by providing identical, interchangeable, and combinable filtration units.
It is another object of the present invention to monitor, sense, alarm or otherwise indicate an end of filter life or the presence of a defective filter. Additional objects and advantages of the present invention will become clear in view of the detailed description and the accompanying diagrams.